1. Field of the Invention
The present invention relates to an improvement of a metal gasket, which is interposed between a cylinder block and a cylinder head of an internal combustion engine.
2. Description of the Related Art
An internal combustion engine has a metal gasket to be interposed and fastened on a joint surface between a cylinder block and a cylinder head so as to be given a sealing function.
Particularly, a sealing in the area surrounding a cylinder opening is important and, if the sealing in this portion is not sufficient, there develops a pressure drop inside a combustion chamber and thus an overheat.
Hence, a bead, which is concentric with the cylinder opening, is provided on an elastic metal substrate which forms the metal gasket and, by utilizing repulsion of the bead which is generated when the metal gasket is fastened by a bolt, the sealing function is given to the area surrounding the cylinder opening.
At this time, in order to prevent a fatigue fracture of the bead, for example, a stopper is provided to a flat portion between the cylinder opening of the metal gasket and the bead so as to control magnitude of bead amplitude.
Regarding an installed position and a shape of the stopper, there is a technology disclosed, for example, in Japanese Utility Model Application Laid-Open No. 2-6855. This technology is such that a full bead is formed on a sheet of the elastic metal substrate and a shim is fixed on a flat surface which is nearer to the cylinder opening than the bead, so that a cylinder opening peripheral portion becomes thicker for a bolt fastening portion.
Further, the technology disclosed in Japanese Utility Model Application Laid-Open No. 62-115562 is such that a full bead is formed on a sheet of the elastic metal substrate and a metal sub-plate is provided in opposition to an convex portion side of the full bead, and the cylinder opening peripheral portion of this sub-plate is folded on the flat portion of the full bead side of the substrate so that, similarly as described above, the cylinder opening peripheral portion becomes thicker for the bolt fastening portion.
These metal gaskets prevent an overall bend of the bead and vibration amplitude at a driving time by a thick plate portion provided on the cylinder opening flat portion of the full bead and, further, are utilized as stoppers which seal combustion gas.
In recent years, miniaturization and weight reduction, increasing output and saving fuel consumption due to the rapid technological innovation of the internal combustion engine have progressed so much. Consequently air-fuel mixture has become leaner and, vibration amplitude of the cylinder head has had a tendency to further escalate by the weight of auxiliary machines as accompanied with rise in combustion temperatures.
In view of the tendency, the prior art has provided a stopper portion of a metal sub-plate on the flat portion between the cylinder opening peripheral portion bead and the cylinder opening peripheral portion. However, due to miniaturization of the engine, a pitch of the cylinder opening has become narrower with a result that the width of the stopper has also inevitably become narrower. For this reason, a contact pressure on the sub-plate partially becomes high contact pressure. Further, due to vibration amplitude as well as volume expansion which are generated by operating the engine, a subsidence gradually develops on a engine surface and, as a result, there arises a phenomenon that the function as a stopper is declined, thereby causing a power depression and a overheat.
The present invention has been carried out in view of the problem and aims to provide the metal gasket which can cope with high performance of the engine.
In order to achieve the object, the outline of the present invention is that a metal gasket is interposed between a cylinder block and a cylinder head and seals between both surfaces, wherein the metal gasket comprises an elastic metal substrate provided with a bead in a cylinder opening peripheral portion; a portion arranged at a convex portion side of the bead, and constituted by a metal thin plate which is thinner than the elastic metal substrate.
According to the constitution, the cylinder opening peripheral portion has high seal contact pressure in contrast to other portions due to the metal thin plate and, moreover, the contact pressure of the cylinder opening peripheral portion becomes uniform.
Further, by fastening the bead further by full compression, stress amplitude of the bead is reduced and fatigue resistance of the bead is improved and irregularity of a cylinder deck surface is covered up by the bead having high seal contact pressure.
Further, in the metal gasket constituted as described above, by forming a bead having the same direction as the bead of the elastic metal substrate on the metal thin plate for the cylinder opening peripheral portion, a bead spring constant of the cylinder opening peripheral portion is enhanced and still higher seal contact pressure can be obtained.
The metal gasket may have a constitution wherein the metal thin plate is arranged among a plurality of elastic metal substrates.
Further, in the metal gasket, the metal thin plate is fixed in the outside area of the bead provided on the cylinder opening peripheral portion of the elastic metal substrate.
The metal thin plate is fastened on the elastic metal substrate at a position from the edge of the cylinder side of a water pore outside of the cylinder of the engine to the distant side edge of the cylinder in the water pore, so that functional influences over the seal contact pressure by a step and a projection of the fixed portion by various fixing methods can be controlled.
The water pore may be of a form interspersed around the cylinder or may be a water jacket continuously formed in a wide range of a cylinder periphery.
Further, in the metal gasket, a slit in the shape of a complete round, an ellipse, a square hole and the like is formed in the elastic metal substrate, and an engaging portion integrally formed on the outer periphery of the metal thin plate is engaged with the slit so as to be fixed on the elastic metal substrate. Regarding the number of fixations when the metal thin plate is fixed, it is fixed at as many places as possible so that its shifting can be controlled during operation of the engine. However, when the processing man-hours is considered, it is desirably fixed at one to six places for one cylinder.
In that case, a passage hole of coolant provided in the elastic metal substrate can be used as the slit.
For the shape of the slit, a complete round, an ellipse, a square hole and the like are widely used, but in order to accurately fix the metal thin plate at the proper position of the elastic metal substrate and, moreover, to prevent the shifting, the slit shape is desirably a complete round or an ellipse.
Further, the metal gasket is deformed into a concave portion (convex portion) which continues in one direction by a press working in a thickness direction and is deformed into a convex portion (concave portion) which is opened in a direction to cross the direction and, moreover, by a coupled portion which is wider than the opening portion opened by pressurizing its base by the press working, the elastic metal substrate and the metal thin plate are integrally coupled.
Regarding the number of couplings when the metal thin plate is coupled, it is coupled at as many places as possible so that its shifting can be controlled during operation of the engine. However, when the processing man-hours is considered, it is desirably coupled at one to six places for one cylinder.
Further, the gasket has the elastic metal substrate and the metal thin plate coupled at a mutual bite portion between the metals, on which a surrounding portion of the deformed base deformed by the press in the thickness direction is side by side.
Regarding the number of couplings when the metal thin plate is coupled, it is coupled at as many places as possible so that its shifting can be controlled during operation of the engine. However, when the processing man-hours is considered, it is desirably coupled at one to six places for one cylinder.
Further, the metal gasket has the metal thin plate joined to the elastic metal substrate by spot welding, laser welding and deposition.
Regarding the number of couplings when the metal thin plate is coupled, it is coupled at as many places as possible so that its shifting can be controlled during operation of the engine. However, when the processing man-hours is considered, it is desirably coupled at one to six places for one cylinder.
Further, the gasket has the metal thin plate fixed on the elastic metal substrate by an adhesive.
As for the adhesive to be used in the present invention, any of a film such as synthetic resin, synthetic rubber or natural rubber or a liquid adhesive comprising those as the chief ingredient is adopted. The adhesive which has a hardness at most 90xc2x0 at a spring type hardness A type test of JIS K6301 is preferable. As specific materials, in the case of rubber materials, there are natural rubber, SBR, NBR, chloroprene rubber, butyl rubber, polysulfide rubber, urethane rubber, silicon rubber, hypelon, acryl rubber, ethylene propylene rubber and the like and, in the case of resin materials, the are selected from urea resin, melanin resin, phenol resin, epoxy resin, vinyl acetate resin, cyanoacrylate, polyurethane, xcex1-olefin-maleic anhydride resin, water high polymer-isocyanate, reaction type acryl resin, denatured acryl resin, vinyl acetate resin emulsion type, vinyl acetate copolymer resin emulsion type, EVA resin emulsion type, acryl resin emulsion type, EVA hot melt type, elastomer hot melt type, polyamide hot melt, synthetic rubber solvent type, synthetic rubber latex type and the like.